[Jet-Lee]

I don't think LOWERING the compression will hurt the redline, since the explosion isn't as hot so it's not as forceful. Redline is determined by what the pistons/rods/crank can take and what the valves can take before floating. If you've got strong enough valve springs so floating isn't a factor, then your only limitation is the strength of parts. In which case, a HIGHER compression will lower your redline due to more pressure = stronger explosion = more heat = more force. I don't think the turbine has any factor in this, as it will spin regardless. As it spins, it will be creating boost which will outweigh any backpressure that may be created.